Optimum Iowa corn planting dates range from mid-April to the end of April in north central and northeast Iowa, and to the first or second week in May in other parts of Iowa (see Table). If we consider the differences between early-planting and late planting, yields are reduced less early in the planting season than late. That means that planting early during the optimum window is generally a better practice than planting a few days after the optimum window. Yields drop off dramatically in mid-May across Iowa. If possible, plant corn prior to May 15 to avoid this "slippery slope" of rapidly reducing yield potential.
One of my colleagues said, "Planting early insures that you won't plant late!" But, we'd both add, that doesn't mean that you won't replant. Be cautious. If conditions remain unseasonably warm in early April, this would be a good year for date of planting studies…on a small scale.
The best thinking on corn planting dates is the understanding that we should begin to plant if:
- Soil conditions are favorable in mid- to late April; AND
- They are expected remain that way for a week or so, or actually improve.
For example, let's say it is April 20 and soil temperatures are in the high 40s and rising fast. Soil conditions are excellent and you've got everything ready to go: the best hybrids, your planter is fine-tuned to perfection, the tractor fueled and you need to do something—and the five to seven day forecast calls for more of the same. Would you plant corn? Most of us without hesitation would say yes.
Let's change one element of that situation: All of the factors just mentioned remain the same but the five to seven day forecast is for cold-wet conditions. In fact it might even snow. Would you plant corn? At this point some of us may get uneasy and shake our heads gently no. Others pound tables and shout, "Of course I'd plant!" Given their individual situations and aversion or fondness of risk, both may be valid responses. What I know is that yield will likely be compromised in the second situation due to the factors mentioned above.
The situation described is very similar to what we actually experienced the second week of April 2011 and in mid-March 2012. Some planted with varied results in early April 2011, but most waited to plant and were pleased they did.
Once we cross the April 11 crop insurance date, if soil temperatures are in the high 40s and rising, plant if soil conditions are favorable and conditions are expected to remain that way for five to seven days, or show improvement.
Table. Recommended planting date windows for Iowa. Based on multiple-location research, Iowa State University.
By Roger Elmore, Department of Agronomy.